To improve visibility by reducing the reflection of ambient light when observing an object to be observed such as displays or printed matters, it is commonly performed to provide, on a surface of the object to be observed, a so-called moth-eye film that has surface asperity (i.e., nanostructures) at a pitch of a visible light wavelength or less. The moth-eye film is also used to be provided on a surface of a light-emitting device or a surface of an optical component such as a lens other than an object to be observed.
Disclosed in WO2012/133943 (Patent Literature 1) is that, to improve the anti-reflective properties of such a moth-eye film, the filling rate of nanostructures is to be 65% or greater and 100% as the upper limit. Here, the filling rate refers to the area of the bottom surface of nanostructures to the area of a unit lattice of the arrangement of the nanostructures that form the moth-eye film.
On the other hand, disclosed in Japanese Patent Application Laid-Open No. 2012-151012 (Patent Literature 2) is a transparent conductive element configured from an optical component having a moth-eye structure and a transparent conductive layer provided thereon, in which the percentage of the area of a flat portion is preferably 0 to 30% in order to provide an improved visibility by reducing wavelength dependency. Here, the percentage of the area of the flat portion is defined to be the ratio of the remaining area obtained by subtracting the bottom area of the nanostructures from the unit lattice area of the moth-eye structure to the unit lattice area.